In an electrophotographic type image forming apparatus (Multi-Functional Peripheral), a visual image obtained by developing a latent image formed on a photoconductor serving as an image carrier using a toner is transferred to a medium (paper or resin sheet). The toner cartridge used in such an image forming apparatus is deemed as a consumable which needs to be replaced with a new one when the residual toner in the toner cartridge runs out.
However, in the case where no sensor is configured in the main body of a toner cartridge to detect the quantity of the residual toner in the toner cartridge, the quantity of the residual toner is estimated through calculation. For example, the quantity of the toner used and the quantity of the residual toner in the toner cartridge are indirectly estimated according to the replenishment time of the toner, the drive time of a processing unit and the count of the pixels printed, and then the residual toner is managed.